Corticobasal degeneration

Corticobasal degeneration


Corticobasal degeneration (CBD) is a rare condition where brain cells become damaged over time and certain sections of the brain start to shrink.

CBD is a progressive condition. This means that the initial symptoms will become more severe over time and new symptoms may also develop.

Initial symptoms of CBD include:

  • sudden problems controlling certain limbs
  • loss of balance and co-ordination
  • slowness and reduced mobility

As CBD progresses, the symptoms will become more wide-ranging and troublesome. They will include:

  • muscle spasms and stiffness
  • an ongoing decline of mental functions (dementia)
  • difficulty swallowing food and liquid (dysphagia)
  • difficulty speaking

Read more about the symptoms of corticobasal degeneration.

What causes CBD?

The brain damage associated with CBD is caused by a build-up of a protein in the brain called tau. Tau is usually found in low levels in the brain, but in CBD it forms clumps that kill nearby brain cells.

This damages vital parts of the brain, such as the cortex and basal ganglia, which are responsible for important functions, including:

  • movement
  • speech
  • higher thought processes, such as planning and understanding

Exactly why tau protein builds up and forms clumps isn’t known.

Read more about the causes of corticobasal degeneration.

Diagnosing CBD

There’s no single test for diagnosing CBD. Instead, a diagnosis will be made based on the type and pattern of symptoms and by ruling out other conditions that can cause similar symptoms, such as a stroke, Parkinson’s disease, motor neurone disease and more common types of dementia.

As CBD shares symptoms with a number of other more common conditions, confirming the diagnosis can be challenging and may take several months, or in some cases years.

Read more about diagnosing CBD.

Treating CBD

There’s no cure for CBD. Several medications, such as memantine, have been suggested to slow down the condition’s progression and improve the function of the brain, but it’s not clear how effective they are.

Most treatments for CBD focus on relieving a person’s symptoms and helping them cope with daily life. These include medication to relax muscles and using feeding tubes to overcome swallowing problems.

Read more about treating corticobasal degeneration.

Complications of CBD

CBD isn’t itself life-threatening, but can lead to serious complications.

Difficulty swallowing (dysphagia) is a common symptom of CBD, which increases the risk of a person choking or inhaling food or liquid into their airway (aspiration).

If this happens, aspiration pneumonia can develop. This is a lung infection that’s triggered when a small piece of food enters the lungs.

Read more about the complicatons of CBD.

Symptoms of corticobasal degeneration

Corticobasal degeneration (CBD) is a progressive condition. This means the symptoms develop gradually and become more severe over the course of many years.

It’s important to realise that only a few people will experience all the symptoms described below. The symptoms will also vary in severity from person to person.

Initial symptoms

One of the typical signs of CBD is difficulty controlling one of your limbs. In most people, it’s usually the hand or arm that’s affected, but sometimes it can be the leg.

You may have muscle stiffness, rigidity and spasms in your limb, and you may find it increasingly difficult to use the affected limb. Some people with CBD have reported that it feels like the affected limb is no longer under their control and doesn’t belong to them. This is known as alien limb syndrome.

Another common initial symptom of CBD is that you begin to lose your sense of balance and co-ordination, which leads to walking difficulties.

Later symptoms

As CBD progresses, it will affect other limbs, usually both your arms and legs.

Your balance and co-ordination will get worse and it’s likely you’ll find it increasingly difficult to walk. Most people have problems with their speech, which will become slow and slurred, making it difficult to understand.

Eye muscles are usually also affected. Many people have problems moving their eyes up and down and sometimes to the left and right. This can increase the risks of falls and cause problems carrying out everyday tasks, such as eating and reading.

At this stage, many people with CBD start to experience symptoms of dementia, including:

  • problems recalling words and expressing yourself using the correct language
  • short-term memory loss and increasing forgetfulness
  • problems carrying out tasks that require planning
  • problems coping with sudden and unexpected situations, such as suddenly realising you’ve forgotten the keys to your house

It’s also common for someone with CBD to experience personality changes and become depressed, apathetic, irritable, agitated or anxious.

A small number of people with CBD also develop obsessive compulsive disorder (OCD).

Advanced stages

As CBD reaches an advanced stage, the symptoms of muscle stiffness and rigidity will continue to get worse, and you may lose the ability to move one or more of your limbs. Some people with advanced CBD are unable to walk and need a wheelchair.

It’s also likely that your speech will continue to deteriorate and people may find it difficult to understand you.

Problems controlling your eye muscles are also likely to get worse. Some people with advanced CBD will not be able to change the direction of their gaze and will only be able to stare straight ahead.

For a small number of people with advanced CBD, dementia will worsen and they’ll need constant care.

Most people with advanced CBD will find it increasingly difficult to swallow food and liquid. This is known as dysphagia. At some point, people with CBD will need to consider the possible benefits and drawbacks of using a feeding tube.

As a result of dysphagia, many people with CBD will experience repeated chest infections caused by fluid or small food particles falling down into their lungs. This can lead to a serious condition called aspiration pneumonia, which is the leading cause of death in cases of CBD.

Read more about aspiration pneumonia.

Causes of corticobasal degeneration

Corticobasal degeneration (CBD) is caused by a progressive loss of brain cells.

It’s one of a group of conditions called ‘4 repeat tauopathies’, characterised by an excess amount of an abnormal protein called tau protein.

In a healthy brain, tau protein is found in low levels, but in CBD the levels increase, forming clumps that are thought to kill nearby brain cells.

This shrinks parts of the brain responsible for movement, speech and higher thought processes, such as planning and understanding.

The symptoms of CBD are similar to those of another condition called progressive supranuclear palsy (PSP). However, in PSP the pattern of brain damage is slightly different. It’s possible that both CBD and PSP are two related syndromes that have the same underlying causes.

It’s not known what leads to the over-production of the tau protein and the resulting death of brain cells.

Genetic link 

One theory is that CBD could be the result of a mutation in the gene responsible for producing the tau protein. This is known as the MAPT gene (microtubule-associated protein tau gene).

A genetic mutation occurs when the instructions found in all living cells become scrambled in some way. This leads to one or more of the body’s processes not working as it should.

There’s evidence that the genetic mutations affecting the MAPT gene are responsible for conditions with similar symptoms, such as some types of dementia and PSP.

However, there’s still no firm evidence to support the theory that mutations in the MAPT gene are responsible for CBD.

Also, as CBD doesn’t run in families, it would appear that the condition isn’t wholly caused by the genes a person inherits from their parents.

One or more environmental factors may trigger CBD in people who are susceptible to it.

Possible factors could include:

  • a virus or other type of infectious agent, which may slowly infect the brain over many years
  • an unidentified neurotoxin (poison that damages the brain and nerve cells) that may be present in the environment

Read more about genetics.

Diagnosing corticobasal degeneration

There’s no single test to help diagnose corticobasal degeneration (CBD).

Instead, the diagnosis is based on the type and pattern of symptoms and ruling out other conditions that can cause similar symptoms, such as a stroke, Parkinson’s disease, motor neurone disease and more common types of dementia.

As CBD shares symptoms with many other more common conditions, confirming the diagnosis can be challenging and may take several months, or in some cases years.

Imaging scans

If you have symptoms that suggest there’s something wrong with your brain, it’s likely you’ll be referred for brain imaging studies.

These may include a:

  • magnetic resonance imaging (MRI) scan – where strong magnetic fields are used to produce a detailed image of the inside of the brain
  • DatSCAN – a test that involves using a small amount of radioactivity to obtain images of an area of your brain; it can help differentiate between brain disorders
  • positive emission tomography (PET) scan – similar to an MRI scan, a PET scan has the added advantage that it can assess how different parts of the brain are functioning

These types of imaging studies can be useful in ruling out other possible causes of CBD, such as a brain tumour or stroke.

They can also detect abnormal changes to the brain that are consistent with a diagnosis of CBD, such as shrinkage in the cortex and basal ganglia.

Ruling out Parkinson’s disease

You may also be prescribed a medication called levodopa. This can help determine whether your symptoms are caused by CBD or Parkinson’s disease.

This is because people with Parkinson’s disease usually experience a marked improvement in their symptoms after taking levodopa. However, this isn’t the case for people with CBD, and levodopa usually only has a limited effect in improving symptoms.

Neuropsychological testing

It’s also likely you’ll be referred to a neurologist (a nerve and brain specialist) and you may need to have neuropsychological testing.

This involves having a series of tests to evaluate the full extent of your symptoms and their impact on your mental abilities. The tests will look at abilities such as:

  • memory
  • concentration
  • understanding language
  • processing visual information, such as words and pictures

Most people with CBD have a distinct pattern in terms of their mental abilities. They often have what’s known as subcortical dementia which affects their planning abilities.

They have poor concentration, a low attention span and problems with spoken language and processing visual information.

Their memory of previously learned facts, such as who was the last prime minister, is usually unaffected.

Receiving the diagnosis

Once all other possible causes of your symptoms have been ruled out, a confident diagnosis of CBD can usually be made.

Being told that you have CBD can be an emotionally devastating experience, and the news can often be difficult to take in. Therefore, at this time, it’s important that you have the support of your family and care team, who will be able to help you come to terms with the diagnosis.

A charity called the PSP Association provides help and support for people with CBD. The charity mainly helps people with progressive supranuclear palsy (PSP), but as the symptoms and treatments of CBD and PSP are similar, the PSP Association also supports people with CBD.

As your symptoms progress, you’ll need full-time care and you may also need assistant technology, such as a wheelchair, to help with activities.

Read more about practical support and adjusting to a disability

Treatment of corticobasal degeneration

There’s currently no treatment to stop or slow down the progression of corticobasal degeneration (CBD). However, many of the symptoms are treatable.

As CBD is a rare condition, you’ll probably be referred to a specialist centre, such as the Institute of Neurology in London.

After discussion with the staff, a care and treatment plan will be drawn up. It will aim to provide you with:

  • relief from the symptoms of CBD when possible
  • support and advice to make your life easier

Your care team

As CBD can have an impact on many different aspects of your life and health, treatment is provided by a team of health and social care professionals working together. This is known as a multidisciplinary team (MDT).

Members of your MDT may include:

  • a neurologist – a specialist in treating conditions affecting the nervous system
  • a physiotherapist – a therapist who helps people improve their co-ordination and range of movement
  • a speech and language therapist
  • an occupational therapist – a therapist who helps people improve the skills and abilities they need for daily activities, such as washing and dressing
  • a psychologist
  • a social worker – they’ll be able to advise you about the support available from social services
  • an ophthalmologist or orthoptist – specialists in treating eye conditions
  • a palliative care specialist – a healthcare professional who specialises in treating people with terminal conditions
  • a specialist neurology nurse – they’ll usually be your first point of contact with the rest of the team


While there’s no medication to treat CBD directly, there are some medications that can help control some of the condition’s symptoms. These are described below.


Memantine is a type of medication known as an NMDA antagonist, which was designed to treat Alzheimer’s disease. It reduces abnormal brain activity, which helps slow the progression of Alzheimer’s disease and improves mental and physical functions.

Some experts have suggested that memantine may have a similar effect in people with CBD. However, there’s limited evidence that memantine is effective or safe in people with CBD. Therefore, you should discuss the potential pros and cons of treatment with memantine (or possibly other medications used to treat Alzheimer’s disease) with your care team.

Side effects of memantine include:


Levodopa is a medication that’s often used to treat Parkinson’s disease. While it’s usually less effective for people with CBD, it may provide short-term improvement in muscle stiffness and rigidity in some people.

Levodopa works by increasing the levels of a brain chemical called dopamine, which transmits messages from your brain that control and co-ordinate your body’s movements. Therefore, an increase in dopamine levels may lead to a corresponding improvement in muscle control.

Two common side effects of levodopa are nausea and indigestion. However, these side effects will usually pass within a few weeks, once your body becomes used to the medication.

Other side effects that can occur if you take levodopa on a long-term basis include:

  • involuntary physical movements, such as jerking
  • confusion
  • mood changes – for example, feeling more anxious
  • drowsiness


Baclofen is a type of medication that can be used to treat muscle stiffness and rigidity. It works by blocking some of the nerve signals that cause muscle stiffness.

Side effects of baclofen may include:

  • dizziness
  • drowsiness
  • constipation
  • diarrhoea 
  • headaches
  • an increased need to urinate

Again, these side effects will usually pass once your body becomes used to the medication.


Clonazepam is a type of medication that can be used to treat symptoms of muscle spasms.

Side effects of clonazepam may include:

  • fatigue (extreme tiredness)
  • muscle weakness
  • dizziness
  • loss of co-ordination
  • light-headedness

As with baclofen, the side effects of clonazepam usually pass once your body has become used to the medication.

You should avoid drinking alcohol while you’re taking clonazepam because it can make the side effects worse, as well as magnifying the effects of the alcohol.


A physiotherapist can give you advice about how to make the most of your remaining mobility by using exercise. Regular exercise can help strengthen your muscles, improve your posture and prevent stiffening of your joints.

Your physiotherapist will also be able to give you advice about any aids that could help you, such as a walking frame or shoes designed to reduce your risk of slipping and falling.

Read more about physiotherapy.

Cognitive stimulation

Cognitive stimulation is a type of therapy that’s used to treat the symptoms of dementia. It involves taking part in activities and exercises that are designed to improve your memory, problem-solving skills and language ability.

Cognitive stimulation is provided by a trained carer and usually consists of two 45-minute sessions a week. During these sessions, you’ll be involved in discussions about a variety of topics, as well as taking part in word and memory games and other activities, such as identifying pictures of famous people.

Occupational therapy

An occupational therapist (OT) can give you advice about the best ways to increase your safety and prevent trips and falls during your day-to-day activities.

For example, many people with CBD benefit from having bars placed along the sides of their bath to make it easier to get in and out.

The occupational therapist will also be able to spot potential hazards in your home that could lead to a fall, such as poor lighting, badly secured rugs and crowded walkways and corridors.

Speech and language therapy (SLT)

A speech and language therapist can help you to improve your speech and swallowing problems. They can teach you a number of techniques to help make your voice as clear as possible.

As CBD progresses, you may need some sort of assistive technology to help you communicate. A range of communication aids is available and your speech therapist will be able to advise you about the devices that will be most suitable for you.

Your speech therapist should also be able to help you if you have difficulties swallowing food and water (dysphagia).

For example, they should be able to teach you exercises to help stimulate the nerves used to trigger your swallowing reflex and strengthen the muscles that are used during swallowing.

A number of physical techniques can also be used to make swallowing easier. For example, some people find that moving their chin forward while swallowing helps prevent food from entering their airways.

Diet and severe dysphagia

As the symptoms of your dysphagia become more severe, you’ll need additional treatment to compensate for your swallowing difficulties.

You may be referred to a dietitian. They’ll advise you about making changes to your diet, such as incorporating food and liquids that are easier to swallow while ensuring you receive a healthy, balanced diet.

For example, mashed potatoes are a good source of carbohydrates, while scrambled eggs and cheese are high in protein and calcium.

Feeding tubes may be recommended in severe cases of dysphagia that increase your risk of developing malnutrition and dehydration. You should discuss the pros and cons of feeding tubes with your family and care team, preferably when your symptoms of dysphagia are at an early stage.

There are two types of feeding tubes. They are:

  • nasogastric tube – a tube is passed down your nose and into your stomach
  • percutaneous endoscopic gastrostomy (PEG) tube – a tube is surgically implanted directly into your stomach, which passes through a small incision on the surface of your stomach or abdomen

Nasogastric tubes are designed for short-term use and last for 10-28 days before they need to be replaced. PEG tubes are designed for long-term use and last for up to six months before they need to be replaced.

Advanced decisions

Many people with CBD make advanced decisions. This is where you make your treatment preferences known in advance in case you’re unable to communicate them at a later stage because you’re too ill.

Issues that can be covered by an advanced decision include:

  • whether you want to be treated at home, in a hospice or in a hospital once you reach the final stages of CBD
  • what type of painkillers you would be willing to take
  • whether you would be willing to use a feeding tube if you were no longer able to swallow food and liquid
  • whether you’re willing to donate any of your organs after you die (the brains of people with CBD are particularly useful for ongoing research)
  • if you have respiratory failure (loss of lung function) due to aspiration pneumonia, whether you’d be willing to be resuscitated by artificial means, such as having a breathing tube inserted into your neck

Read more about advanced decisions. Your care team will also be able to give you more information and advice about making decisions.

Complications of corticobasal degeneration

Aspiration pneumonia is a potentially serious complication of corticobasal degeneration (CBD).

Aspiration pneumonia is a lung infection that’s triggered when a small piece of food enters the lungs.

People with CBD are particularly vulnerable to aspiration pneumonia because their impaired swallowing reflexes mean that their larynx (voice box) doesn’t close when they swallow. This leaves their lungs unprotected.

The symptoms of aspiration pneumonia include:

  • high temperature (fever) of 38C or above
  • fatigue (extreme tiredness)
  • chest pain
  • shortness of breath 
  • blue skin (cyanosis) due to a lack of oxygen
  • wheezing

You may also have a cough that sometimes produces foul-smelling phlegm and may contain traces of blood and pus.

Contact your care team immediately if you’re being treated for CBD and you develop these symptoms. If this isn’t possible, contact your local out-of-hours service or call NHS 111.

The symptoms of aspiration pneumonia can range from mild to severe. In severe cases, admission to hospital will be needed so that intravenous antibiotics can be given.

In particularly vulnerable or frail people, there’s a chance that the infection could cause their lungs to become filled with fluid, preventing them from working properly. This is known as acute respiratory distress syndrome (ARDS)

As most people with advanced CBD are vulnerable and frail, repeated episodes of aspiration pneumonia often result in ARDS and then death.